It is frequently required in telephony test equipment to convert accurately an a.c signal to a corresponding d.c. (full-wave rectified) voltage; this conversion is commonly called precision rectification and is achieved using a precision rectifier circuit.
Ideally, a precision rectifier circuit has perfect symmetry, so that it converts equal magnitude but opposite polarity half cycles of the a.c. signal to equal magnitude pulses of the full-wave rectified output voltage. However, known precision rectifier circuits suffer to some extent from non-symmetry, which may be caused by different gains from the input to the output for the respective polarities, or by offset voltages of amplifiers used in the precision rectifier circuit. Non-symmetry arising from the former cause results in a constant percentage error for all levels of the a.c. input signal, and in some cases may be tolerable. Non-symmetry arising from the latter cause results in a percentage error which increases as the level of the a.c input signal is reduced, and which is often the limiting factor in determining the dynamic range of the circuit. The dynamic range is the range of input magnitudes over which the circuit functions within a given accuracy.
The operation of precision rectifier circuits is also affected by other factors such as amplifier output voltage slew rates and the switching, storage, and reverse recovery times of diodes and transistors used in the circuits; in particular these factors limit the highest frequency at which the circuit can be used within a given accuracy.
In order to improve the performance of precision rectifier circuits, resort has been made to the use of closely matched components such as resistors, transistors, and diodes, but this results in an undesired increase in the complexity and cost of the circuits.